Preheat the Oven: Preheat your oven to 180°C (350°F). Grease the muffin tray lightly with oil or cooking spray to prevent sticking.
Prepare Egg Mixture: In a large bowl, crack the eggs and whisk them well until smooth. Add milk, salt, black pepper, and garlic powder. Mix until fully combined.
Add Fillings: Add chopped vegetables, cooked chicken (if using), and shredded cheese into the egg mixture. Stir everything evenly.
Fill Muffin Tray: Pour the mixture into each muffin cup, filling about 3/4 full to allow space for rising.
Bake: Bake in the preheated oven for 18–22 minutes, or until the eggs are fully set and lightly golden on top.
Cool and Serve: Remove from oven and let cool for 5 minutes. Carefully take out the muffins and serve warm or store for later.